wx_controls: fix workaround

this workaround in 1f343f1ea858a652716599474d64dc691c0ab60d introduced #362.
Instead of creating a new instance of an incompatible class I fixed the height in gcULProgressBar directly.

This bug was caused, because gcULProgressBar had a uint8_t field, which resulted into some errors within glibc.

This pull request will fix both #362 and #408

NOTE: this is a candidate for the stable branch